DESCRIPTION: (Applicant's abstract) This application is focussed on bombesin receptors in frog and in rat. Four mammalian bombesin receptors have been identified; one binds gastrin-releasing peptide (GRP) with highest affinity, another binds neuromedin B (NMB) with highest affinity, the third is an orphan receptor which binds the known bombesin-like peptides with low affinity, and the fourth has recently been isolated by the applicant. In addition, there is evidence that at least one additional form, and possibly several additional forms, of the bombesin receptor exists; these additional forms are highly related to the recently identified fourth receptor form. The studies proposed in this application will further characterize the forms of the bombesin receptors in both frog and rat. cDNA clones will be expressed in cell lines and in Xenopus oocytes and the properties of the receptors determined. Existing peptides will be tested as agonists and antagonists for the various receptor forms. Finally, these agonists and antagonists will be injected into rats and the effects of several behaviors will be examined, with a focus on body temperature and grooming. These studies will provide a better understanding of the physiological function of the various bombesin receptors.